title: Hypoxia regulates the proliferation and osteogenic differentiation of human periodontal ligament cells under cyclic tensile stress via mitogen-activated protein kinase pathways.
abstract: BACKGROUND
  Previous studies have shown that periodontal ligament exists in a hypoxic microenvironment, especially under the condition of periodontitis or physical stress. The present study is designed to investigate the effects and mechanisms of hypoxia on regulating the proliferation and osteogenic differentiation of human periodontal ligament cells (hPDLCs) under cyclic tensile stress (CTS).
  
  
  METHODS
  hPDLCs were cultured in 2% O2 (hypoxia) or 20% O2 (normoxia) and then subjected to a cyclic in-plane tensile deformation of 10% at 0.5 Hz. The following parameters were measured: 1) cell proliferation by flow cytometry; 2) cell ultrastructure by transmission electron microscopy; 3) expression of hypoxia-inducible factor-1α (HIF-1α) and osteogenic relative factors (i.e., secreted phosphoprotein 1 [SPP1; also known as bone sialoprotein I/osteopontin], runt-related transcription factor 2 [RUNX2], and transcription factor Sp7 [SP7]) by real-time polymerase chain reaction and Western blot; and 4) involvement of mitogen-activated protein kinase (MAPK) signaling pathways by Western blot with specific inhibitor.
  
  
  RESULTS
  Proliferation index in the hypoxia with CTS group was significantly higher than in other groups. Significant increases in HIF-1α, SPP1, RUNX2, and SP7 occurred in the presence of hypoxia for 24 hours. In addition, MAPK inhibitor (PD 98,059) significantly attenuated hypoxia and CTS-induced phosphor-ERK1/2 (extracellular regulated kinase 1/2), phosphor-JNK (c-jun N-terminal kinase), and phosphor-P38 expression.
  
  
  CONCLUSIONS
  Hypoxia regulates CTS-responsive changes in proliferation and osteogenic differentiation of hPDLCs via MAPK pathways. Hypoxia-treated hPDLCs may serve as an in vitro model to explore the molecular mechanisms of periodontitis.
authors.affiliation: Institute of Stomatology, Nanjing Medical University, Nanjing, China.
authors.forename: Lu
authors.initials: L
authors.lastname: Li
authors.forename: Min-xuan
authors.initials: MX
authors.lastname: Han
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.forename: Yan
authors.initials: Y
authors.lastname: Xu
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
mesh_terms: D000293:Adolescent; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology*; D049109:Cell Proliferation; D002478:Cells, Cultured; D060833:Cellular Microenvironment / Q000502:physiology; D002648:Child; D050659:Core Binding Factor Alpha 1 Subunit / Q000032:analysis; D005260:Female; D005419:Flavonoids; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000032:analysis; D048031:JNK Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D020935:MAP Kinase Signaling System / Q000502:physiology*; D008297:Male; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors; D010012:Osteogenesis / Q000502:physiology*; D053495:Osteopontin / Q000032:analysis; D010513:Periodontal Ligament / Q000166:cytology* / Q000503:physiopathology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D000076182:Sp7 Transcription Factor; D013718:Tensile Strength; D013997:Time Factors; D014157:Transcription Factors / Q000032:analysis; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D005419:Flavonoids; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D047428:Protein Kinase Inhibitors; C493709:RUNX2 protein, human; C506895:SPP1 protein, human; D000076182:Sp7 Transcription Factor; C478163:SP7 protein, human; D014157:Transcription Factors; D053495:Osteopontin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one